The present invention relates to reaction mixtures of organic polyisocyanates, organic polyepoxides and special catalysts that are curable by the action of heat to plastics having isocyanurate and oxazolidinone groups.
Plastics having isocyanurate and oxazolidinone groups are known. They are produced by polyaddition of polyfunctional 1,2-epoxides with polyisocyanates and use of curing catalysts. See, e.g., German Offenlegungsschrift 3,323,153 (believed to correspond to U.S. Pat. No. 4,582,723), European Patent 130,454 (believed to correspond to U.S. Pat. No. 4,564,651), German Offenlegungsschrift 3,323,084 (believed to correspond to U.S. Pat. No. 4,631,306) and German Offenlegungsschrift 3,323,123 (believed to correspond to U.S. Pat. No. 4,562,227). Tertiary amines and imidazoles as well as onium salts and Lewis salts, for example, are suitable catalysts.
German Offenlegungsschrift 3,904,156 (believed to correspond to U.S. Pat. No. 5,084,544) describes the polyaddition of these materials with tertiary amines at room temperature, which leads to dimensionally stable plastics. These materials have a low solubility e.g. in MEK and are no longer fusible, which is an indication that the reaction has progressed beyond the so-called B-stage.
For many fields of technical application, there is a desire for this B-stage, in which the material is a still sufficiently reactive solid that, being grindable, fusible and soluble, covers a wide field of application.
It was the problem of the present invention to produce, in a technically simple way, a solid resin in the B-stage in storage-proof form from the liquid starting compounds .
German Offenlegungsschrift 3,323,123 describes how this B-stage is obtained by thermal initiation of the catalyzed polyaddition. On reaching the B-stage, this polyaddition is stopped by addition of a catalyst poison.